Help Please - PJ bass - when tone @ 20% volume cuts completely

Discussion in 'Pickups & Electronics [BG]' started by Arch1medes, Jul 26, 2020.


  1. Arch1medes

    Arch1medes

    Nov 14, 2009
    Just re-soldered everything on the control plate, and put in a new cap. When I cut the tone down to say, 20% left, volume cuts completely. Bass is a PJ setup.

    I played around with the grounding using alligator clips and even swapped out the tone pot for a new one and have the same issue. This happens with the control plate separated from the body but still connected AND when it’s inserted & screwed back on. No change.

    I’m under the assumption I don’t need housing wires going from pot-to-pot ( or the input jack) since the copper shielding on the control plate acts as a common ground?

    The bridge ground wire + both pickup’s grounds are twisted together and soldered to the back of the tone pot housing.

    This is my first attempt at hands-on electronics (not just theory or ideas) so any help is appreciated.

    C1CBE298-7592-49ED-92B0-65FBFB1863E7.jpeg
     

    Attached Files:

    Last edited: Jul 26, 2020
  2. tonymcbony

    tonymcbony

    Mar 21, 2006
    Can you show the wiring on the tone as well?

    Did you use a diagram?

    jbass.gif

    I would still ground the back of the pots as they’re being used as a part of the circuit.

    Have a look at the value of the pot too, and whether it’s a linear or log/audio
     
    Last edited: Jul 27, 2020
  3. Arch1medes

    Arch1medes

    Nov 14, 2009
    thanks for replying! I’ll try your diagram today. The star ground (pickup, pickup, bridge) is soldered to the back of the 2nd volume knob, and the tone cap is on lug 3 & tone pot casing.

    Question: looking at your diagram, does the star ground have to share the same solder bead as the tone cap?
     
  4. dwizum

    dwizum

    Dec 21, 2018
    The star ground certainly does not "have" to share the same solder bead.

    Do you own a multimeter? You can use one in continuity mode to check if your grounds are good and if your signal path is intact, and you can also use one in resistance mode to watch resistance on the pots are you turn them.

    I know you said you replaced the tone pot already, but that would be my first thought - I've had pots that failed just like you're describing. I'd be curious to check the pot's resistance as you turned it (ideally out of circuit).
     
    tonymcbony likes this.
  5. Arch1medes

    Arch1medes

    Nov 14, 2009
    As soon as things slow down at work I’ll run a resistance test on the pot w\ cap out of circuit.

    Yes, I do have a multimeter and have good, open readings on the following:
    • Cap (by itself & installed)
    • All pot casing & input jack & shielding combinations
    • All segments on the white-wire path
    Again, no pot-to-pot or input ground wires since the shielding is acting as a ground.
     
    MrMoonlight likes this.
  6. Arch1medes

    Arch1medes

    Nov 14, 2009
    correcting myself from earlier: star ground is soldered to the tone pot
     
  7. Arch1medes

    Arch1medes

    Nov 14, 2009
    The picture I uploaded yesterday showed an orange cap, but it stopped working, so now I’m using a ceramic cheapie.

    Here we go!

    B8E7F49E-AB89-4943-83F5-530AA44704CA.jpeg DB902B78-7EE3-41BE-8217-F4841A23D688.jpeg 308716D1-188A-4075-AAAF-904F4FBAEC4C.jpeg B6261186-30F0-410B-A298-6C8717B9D47D.jpeg BC7684D9-E8AE-43B4-BCE5-905CF520CB80.jpeg F5BF979A-0821-4AB8-B592-4549D05BAB83.jpeg 511916F7-E079-4CF2-8B01-0426EFE04A89.jpeg 782AAF42-F922-444C-8822-E99B7CBF8205.jpeg
     
  8. Arch1medes

    Arch1medes

    Nov 14, 2009
    Resolved

    After looking at the diagram in reply #2 from tonymcbony and comparing about a dozen others (both bass AND guitar) I noticed all of them had the input grounded EVEN if the control plate, or entire pickguard, was shielded.

    exhibit A:
    0C51CFE3-F5C5-4758-9066-D2548177843E.jpeg

    so I made the following changes:
    BDBF3C7A-A72C-47B7-B97E-4E4392A01F82.jpeg
     
    tonymcbony and Matt Liebenau like this.
  9. tonymcbony

    tonymcbony

    Mar 21, 2006
    Nice work! Glad to see you sorted it
     
  10. I followed the link from the other thread. I saw the first pic here and said to myself where is the ground on the jack. Glad you figured it out.
     
  11. Arch1medes

    Arch1medes

    Nov 14, 2009
    Yes, thank you. I was stuck on the idea that with everything shielded all components share a common ground. I still don’t fully understand why this worked, I’m just accepting that it did.
     
    Funkdified likes this.
  12. Arch1medes

    Arch1medes

    Nov 14, 2009
    thank you! I’ve learned a lot these past few weeks

    63B67991-55E2-412C-9E5C-F4A33E278890.jpeg
     
  13. dwizum

    dwizum

    Dec 21, 2018
    The shielding should be grounded, and the jack being screwed against the shielding should ground it as well. Of course there may have been some bad contact to the shielding which you cured with that ground wire. Or you may have had a short on the lead for the cap which you insulated.

    Might want to check for continuity between your shielding and ground (at the jack), just in case. If the shielding isn't well grounded it's not going to be effective.
     
  14. Arch1medes

    Arch1medes

    Nov 14, 2009
    Yes, I did successful continuity tests from each component’s “earth” to the shielding (several times when my sanity was at its lowest)

    My hunch lines up with what you mentioned, that it was cap related. The first one failed from amateur soldering mistakes and the 2nd cap (ceramic) had been stored in a drawer for 5 years. Even though it tested fine on the multimeter, I just didn’t trust it so I ordered a new one.
     
    Last edited: Jul 31, 2020
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